This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Ankylosing spondylitis (AS) is a chronic inflammatory arthritis that primarily affects the joints of the pelvis and spine. Inflammation in these joints causes pain, stiffness, and limitations in spinal flexibility. Over time, fusion of the joints occurs, leading to complete spinal immobility, secondary osteoporosis, and risk of fracture and spinal cord injury. Peripheral joints may also be involved. The prevalence of AS is 1:1000 persons, and it primarily begins in young adulthood. Men are affected 3 times more often than women. AS is the disease most tightly linked to any marker in the HLA locus, and susceptibility to AS is largely genetically determined. Eligible patients will undergo a simultaneous screening and baseline visit at which time their diagnosis of AS will be confirmed by the study investigators, a Background Information Questionnaire and pain scale will be completed, and phlebotomy will be performed. At this time they will be asked to: 1.) complete an Arthritis Activity Questionnaire;2.) complete a Psychosocial Adjustment Questionnaire;3.) have a physical examination of their joints and measurements of spinal flexibility;4.) have 50 ml of blood drawn for genotyping;5.) have blood drawn for ESR (sedimentation rate) and CRP (C-Reactive Protein). Both are measures of inflammation;6.) have radiographs of the pelvis (AP view), lumbar spine (AP and lateral views), and cervical spine (lateral view). Patients that have been enrolled in the PSOAS study will continue to be followed in this study. In addition, we plan to enroll approximately 360 patients newly acquired and recruited for this study at 4 different sites around the country: CSMC, University of California at San Francisco, University of Texas at Houston and the National Institutes of Health. At CSMC, we plan to enroll 120 of those patients. Subjects will be consented for participation by the Principal Investigator when they arrive for their screening/baseline visits in the General Clinical Research Center. Follow-up visits will occur every 6 months after the baseline visit and continue for the length of the study for each patient. Patients will vary in the length of the follow-up period from 2 to 7 years during the time frame of this study because we will be following previously enrolled patients as well as newly acquired patients. At each visit, participants will complete the Arthritis Activity Questionnaire, the Psychosocial Adjustment Questionnaire, have an examination of their joints and measurements of spinal flexibility, and have blood drawn for sedimentation rate and C-reactive protein (measures of inflammation). Radiographs will be repeated every 24 months. Phlebotomy and radiographs will be performed at the enrolling center. All blood samples obtained for this study will be sent for analysis to Dr. John Reveille at the University of Texas at Houston. Testing of ESR and CRP will be done at a commercial laboratory. Serum and plasma for future biomarker analyses will be aliquoted and stored in a -70C freezer at each site for future analysis. All questionnaire and clinical data will be sent to Dr. Michael Ward for analysis at the NIH. Radiographs will be taken digitally, mailed to CSMC on CD and scored by Dr. Thomas Learch, the consulting bone radiologist from USC.